Hunter syndrome or mucosaccharidosis type II is a lysosomal storage disease (LSD) in which mucopolysaccharides, also known as glycosaminoglycans (GAG), are not broken down correctly and build up in the body due to a deficiency of IDS. As GAG continues to buildup throughout the cells of the body, various signs of Hunter syndrome become more visible. Physical manifestations for some people with Hunter syndrome include distinct facial features and a large head. Representative among the symptoms of Hunter syndrome are an enlarged abdomen due to hepatomegaly or splenomegaly, deafness, valvular heart disease, obstructive airway disease and sleep apnea. Also, major joints may be affected by Hunter syndrome, leading to joint stiffness and limited motion. In some cases of Hunter syndrome, central nervous system involvement leads to developmental delays and nervous system problems. Hunter syndrome is a known to occur at a rate of 1 in 162,000 and is a genetic disorder in the form of chromosome X-linked recessive and so given the great suffering to the family as well as the patient.
Various trials have been carried out thus regarding the treatment of Hunter syndrome, including bone marrow graft, enzyme replacement, and gene therapy. While bone marrow graft is able to stop most of the symptoms, it is difficult to find an HLA (human leukocyte antigen) match for all patients. Further, a bone marrow graft is a major surgical operation accompanied by several adverse effects, including the patient's life being put under high risk if the HLA is mismatched. Gene therapy for Hunter syndrome delivers a normal IDS gene into the body with the aid of a viral vector such as adenovirus or retrovirus or a non-viral vector. However, gene therapy remains an experimental technique, and has not been clinically applied. As for the enzyme replacement treatment for Hunter syndrome, it administers externally produced IDS and has the advantage of being simple. However, enzyme replacement must be continuously carried out, which incurs a high expense. Elaprase® (Shire Pharmaceuticals Group), produced using recombinant DNA technology, was approved by the FDA as an enzyme replacement treatment for Hunter syndrome. However, this drug is very expensive and suffers from the drawbacks of being poor in effect and safety.
As described above, although various therapies for Hunter syndrome have been developed, there is still a pressing need for a new therapy and agent that exhibits high therapeutic efficacy with high safety.